Cassava is
a commonly produced tuber crop in Africa. It can be used as food, as
a cash crop, as feed for animals and as a source of industrial
raw material. In sub-Saharan Africa, cassava is
mostly used for human consumption in various forms ranging from
boiling the fresh tuber to processing it into cassava flour. Cassava
tubers are an important source of carbohydrates, while the leaves,
eaten as a vegetable, are a good source of protein and vitamins.
Establishment
of the Cassava farm
In
organic farming, crop management begins by giving the plants good
growing conditions through improving soil fertility, and healthy
planting material. This allows the crop to grow healthier, and
produce higher yields.
Suitable
varieties for organic production
Cassava
varieties differ with regard to yield potential, flesh colour (white
or yellow-fleshed), diameter and length of the tubers, disease and
pest resistance levels, time from planting to harvest, cooking
quality and taste. Some cultivars require 18 months or more from
planting to harvest, while others are ready to harvest in 9 months.
Most cultivars have been selected by farmers under their growing
conditions based on yields and cultural tendencies. Each growing
region has its own special cultivars with farmers, often growing
several different cultivars in the field at the same time.
Selection of an appropriate planting site
Cassava
is drought tolerant, can grow on most soils, and gives some yields
even on poor soils where most other crops fail. However, high yields
are obtained in areas with well-drained, loamysoils,
well-distributed annual rainfall of 1,000 to 1,500mm, and warm and
moist climatic conditions only. The best site for planting cassava is
flat or gently sloping land. Steep slopes are susceptible to erosion
and are, therefore, not very suitable areas for growing cassava.
Valleys and depression areas are also not recommended because they
are prone to water logging. Cassava is sensitive to water logging and
heavy soils do not allow the crop’s roots to proliferate and
develop.
Land and seedbed preparation
In
cassava cultivation, it is important to till the land to loosen up
the soil, improve soil drainage and make it easy for roots to
develop. The level of tillage required for the cassava field mainly
depends on the soil type and the drainage at the selected site. In
places with shallow soils or
poorly drained clayey soils, it is important to make mounds or ridges
onto which the cassava is planted, as it encourages better root
development and yields. In sandy soils, only minimum tillage is
necessary and the cassava can be planted flat into the soil, as the
soil is sufficiently loose to allow root development.
Preparing good quality planting material
Cassava
is propagated by planting pieces of the stem (stem cuttings). The
development of cassava and amount of yields depends on the quality of
stem cuttings. There are several cassava pests and diseases, which
are stem-borne. Selecting healthy stem cuttings reduces the spread
and damage caused by pests and diseases.
Recommendations to farmers in selecting good cassava stem cuttings
- Select planting material from healthy growing, high-yielding, 8 and 18-month old cassava plants. Healthy cassava plants have robust stems and branches, lush foliage, and minimal stem and leaf damage caused by pests and diseases.
- From each plant, select the middle, brown-skinned portion of stems as stem cuttings. The stems should be 2 to 4cm thick. These parts sprout and ensure plant vigour better than the top green stem portions. Stem cuttings taken from the top green portions or extreme top and bottom portions of stems are unsuitable. They will dehydrate quickly, produce unhealthy sprouts, and are easily damaged by pests and diseases.
- Tie the stems in bundles and wait for at least 10 days before planting them. The harvested stems can be stored for over 2 months in dry, well-ventilated, shaded areas away from direct sunlight until it is time for planting. One simple method of storing stems consists of arranging them vertically under a shady tree, with the oldest part of the stem buried in the soil. The soil should be moist to keep the stems ‘alive’ as leaves will form on the upper part of the stems. After storage, discard the top and basal parts of the stems, and use the middle part as cuttings. Another method, mainly used under cold conditions, consists of storing the stems in underground tunnels, which are protected from water. The stems are placed inside the tunnel on top of a layer of dry straw, and then covered with another layer of straw and soil.
Planting
To
get the best sprouting and growth from cassava stem cuttings, the
following considerations are recommended:
. Selection
of suitable planting dates.
Planting cassava early, at the
beginning of the rainy season, ensures healthy sprouting and good
plant establishment. This enables the plant to withstand attack by
diseases and pests later in the season.
. Preparation
and handling of stem cuttings.
When cutting up cassava stems
into pieces for planting, each cutting should be between 20 and 30cm
long and have about 5 to 8 nodes, where roots and shoots originate.
The interval between cutting of the stems and planting into the
ground should be as short as possible to avoid dehydration and poor
performance. Soaking the stem cuttings before planting in warm water
(50°C) by mixing equal volumes of boiling and cold water for 10
minutes just before planting prevents stem-borne pest attacks.
. Adopt
suitable planting mode according to the type of soil.
Cassava
cuttings can be planted by hand vertically, at an angle (inclined) or
horizontally, depending on soil types. The drier the soil, the bigger
the part of stem placed in the soil. The vertical planting method is
best suitable in sandy soils and consists of planting the cuttings
vertically with two-thirds of the length of the cutting below the
soil. Planting at an angle is most suitable in loamy soils and
consists of planting the stem cuttings vertically and with an angle
ranging from slightly above horizontal to about 45°. Horizontal
planting is recommended for dry climates and consists of placing the
entire stem cutting horizontally in the soil at a depth of about 5 to
10cm. The spacing between the cassava plants depends on several
factors such as the variety used, the soil type, soil fertility and
water availability and on whether cassava is grown alone (mono crop)
or with other crops (intercrop). If cassava is grown alone, a
distance of 1mt between the plants should be considered. If cassava
is grown as an intercrop, the distance between the crops should range
from 1 to 4mt depending on the branching habit of both the cassava
and other crops to make sure there is enough space for the plants.
Intercropping
Due
to the fact that cassava has a slow initial
development, intercropping during
early crop development is feasible, and helps reduce soil erosion.
However, farmers should consider that cassava is a poor competitor
and can easily be shaded out by tall intercrops like maize. For this
reason, it is important to consider the branching habit of both the
cassava and the other crops in the intercropping system and make sure
there is enough space for both crops. Furthermore, cassava can suffer
from nutrient and/or water competition from intercrops. Therefore,
attention must be given to the intercropping species that have
different root systems and nutrient requirements.
Farmers
usually intercrop cassava in simple or complex mixed cropping systems
with vegetables such as amaranth and okra,
plantation crops such as coconut, coffee, maize or legumes, and
pulses such as cowpea and groundnuts. The intercropping pattern
depends on the environmental conditions, food preferences and market
conditions of the region.
Simple
mixtures consist of the intercropping of only two crops, in which
farmers select arable crops on the basis of differences in growth
habit and time of maturity. For example, cassava, which is a
long-duration crop with 9 to 18 months to maturity, is often
intercropped with short-duration crops with 2 to 5 months of maturity
process, such as maize, cowpeas, groundnut, okra and
melon. These crops mature when the cassava is just attaining its
maximum leaf area development and thus is able to expand its root
tubers without competition. In complex mixtures consisting of three
or four crops, good yields have been obtained with the following
combinations:
.
Maize - Cassava - Melon
.
Maize - Groundnuts - Cassava
.
Maize - Cassava - Okra - Cowpea
.
Maize - Beans - Cassava
Complex
mixtures improve weed suppression, reduce soil temperature, retain
soil moisture in the topsoil, and produce more organic matter than
single cropping or simple mixtures. Nutrient loss from erosion in
complex mixtures is less than in single cropping.
Crop
rotation
The
continuous planting of cassava in the same field year after year
leads to increased disease and pest levels, reduced yields and crop
failure. To avoid such development, organic farmers should wait for
at least 2 years before planting cassava on the same field again and
develop a crop rotation system. A rotation system generally
improves soil fertility, reduces soil erosion and helps to control
diseases and pests. The suitable crop rotation depends on several
factors such as the climatic conditions, the market requirements and
the skills and objectives of the farmer. However, within a pattern of
crop rotation, cassava is often grown in sub-Saharan Africa at the
end of the sequence, as it can still produce relatively well at lower
fertility levels, where other crops would not grow well.
This
practice leads to lower cassava yields. It is important to establish
a balanced crop rotation, which maintains or improves soil fertility,
and to give cassava a place in the rotation that corresponds to
farmer expectations. Cassava is a good crop to follow such crops as
pumpkin, squashes, maize, sorghum or improved fallow. A 3-season
rotation example that can be used in organic cassava production is
maize-beans / cassava / groundnuts.
Reducing
postharvest losses
Post-harvest
handling of organic cassava aims at maximizing tuber quality by
minimizing any damage or cuts on the tubers during harvesting and
transportation of the tubers. Young leaves and shoots of cassava are
also harvested to be consumed as vegetables and may be as important
as tubers for generating income. However, excessive harvesting of the
leaves can have a negative effect on the yield of tubers.
Early-maturing
cassava varieties are ready for harvesting at 7 months, while
late-maturing varieties are ready 12 months after planting. The
proper stage for harvesting is when the leaves turn yellow and fall
down and the roots are mature. It is advisable to harvest cassava
once it is mature. If the tubers are left in the ground over long
periods, they lose quality and become woody due to hydrolysis
of starch to sugars. Care should be taken to avoid damage
to the tubers during harvesting. Damaged roots are highly susceptible
to fungal attacks and decay.
Harvesting
cassava tubers is labour-intensive and done by hand. It is easy if
the soil is sandy or during the rainy season, but in heavier soils or
during the dry season, harvesting usually requires digging around the
tubers to free them of the covering soil and then lifting/pulling the
plant. The day before harvest, the plants are normally ‘topped’;
the stalks are cut off 40 to 60cm above ground and piled at the side
of the field. From this material, the stalks for the next planting
are selected. Excess soil is then scraped off from the tubers by
hand. This should be done carefully so as not to peel or damage the
outer protective skin of the tubers.
Transportation
The
first thing to be done after the harvest is to transport the tubers
from the production and harvest field to the processing and
utilization site. This is because fresh cassava is highly perishable
(within 2 to 3 days after harvesting). Transportation of cassava
tubers should also be done carefully to avoid bruising and
dehydrating the cassava tubers, especially if it is meant for fresh
consumption.
